Fig. 1

Representative EM images of presynaptic axon terminals from 3 different cases diagnosed with Alzheimer disease (A, B, C) and 3 different non-AD control cases (D, E, F). Presynaptic terminals are colored light blue and the dendritic spines are colored light yellow if present. Arrows mark enlarged or dense cored vesicles and white arrowhead marks a docked synaptic vesicle. While not every presynaptic axon terminal analyzed contained mitochondria, these images demonstrate both intact mitochondria (iM) and damaged mitochondria (dM). Case labels denote the age of the individuals and case details are listed in Table 1. No difference was noted in preysnapse size between the AD and control groups (G, p = 0.26). The AD cases have significantly fewer vesicles/µm² axon area compared to non-AD cases (H, p < 0.01). There is no difference in the % of docked RRP vesicles between AD and control cases, however a greater % of vesicles are in the reserve pool in the control cases (I, p < 0.001). The AD presynapses have fewer vesicles with a diameter of 40 nm or less (J, p < 0.05) and have more vesicles larger than 40 nm (J, p < 0.05). The percent of presynaptic axonal boutons with either enlarged or dense cored vesicles is also higher in the AD cases compared to non-AD group (K, p < 0.0001). Data are Means ± S.E.M. of six AD and six control cases. Student t test (G, H, J) or one-way analysis of variance (I, K). *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001